1. Field of the Invention
The present invention generally relates to a fan controller for an electronic system (e.g., a computer). More particularly, the invention relates to cascadable fan controllers in which a fault with one controller can be provided to the other controller without involvement of external controlling logic such as the system's host controller.
2. Background of the Invention
Many types of electronic equipment, such as computers, include one or more fans to move air through the equipment to thereby help cool the device. Some computers that use a large amount of power require a commensurate number of fans. It is not uncommon for some multiprocessor computers, for example, to include six or eight fans in one enclosure.
Each fan typically is driven by logic called a “fan controller.” Fan controller logic may be implemented as discrete logic on the main system board or as a separate integrated circuit on the system board. Early on, each fan controller was able to control only one fan. Thus, multiple fan controllers were included in a system in which multiple fans were needed. In these configurations, it was up to the host processor to control the operation of the various fans by communicating independently with each fan controller. For example, in a system which included two fans with one fan spinning and the other fan included for redundancy, if the operational fan failed and such failure was detected by the host processor, the host processor would have to direct the redundant fan through its controller to begin operation.
Although generally satisfactory, it may not always be possible for the host processor to control the operation of one fan controller based on a fault condition of another fan. The host processor, for example, may be non-functional. If the host processor is non-functional and the primary fan is not spinning or not spinning sufficiently, there will not be a way to activate the backup fan. In general, it is not always satisfactory to rely on the host processor for controlling the operation of the fan controllers in a system. A better methodology is needed.